Conventionally, a carbon nanotube (CNT) refers to an allotrope of carbon which is abundantly present on earth. CNT is a tube-shaped material wherein one carbon atom binds to another carbon atom thereby forming a hexagonal honey-comb structure. It also refers to an extremely tiny material with a diameter of its tube being a few nanometers (nm=1/1,000,000,000).
Carbon nanotubes in general have excellent mechanical property, electrical property, ability to discharge electric field and hydrogen storing ability with high efficiency. It is known as a nearly perfect material having almost no defects. Carbon nanotubes can be manufactured by using an advanced synthetic technique such as electric discharge method, a pyrolytic method, laser-mediated vacuum evaporation, chemical evaporation by plasma, thermo-chemical evaporation, an electrolytic method, and flame synthesis.
In practice, carbon nanotubes may be applied to almost all fields including astronautics, bioengineering, environmental energy, material industry, pharmaceuticals, pharmaceutical medicines, electronic computers, securities and the like. For example, a carbon nanotube transistor is one of the carbon nanotube products.
The carbon nanotube transistor is composed of a source, a drain and a gate, wherein its channel domain is made of a carbon nanotube.
Carbon nanotube constituting the channel domain of the above carbon nanotube transistor has a few advantages as follows. First, it has excellent electric and thermal conductivities while maintaining the properties of a semiconductor or a metal, thus having a highly efficient heat emission. Further, carbon nanotubes are light-weighted but have mechanical strength 100 times stronger than that of steel, hardly react with other compounds due to their unique chemical properties thus enabling a very stable operation of electronic elements. Therefore, researches have been focused on developing new applied elements and such efforts have been extended recently to medical and biotechnological fields.
Due to the recent trend of aging society and extended life span of people worldwide, there has been a growing concern on the importance of how to manage a healthy individual life. Accordingly, the necessities for an early diagnosis of severe diseases such as cancers and other life-threatening diseases have been emphasized and thus it has been in urgent need to develop a medical device/equipment for frequent self-diagnosis of medical conditions with reduced cost and time, whenever deemed necessary. In this context, it appears very important to find a method to detect and identify the presence of any specific molecules (such as proteins, peptides, amino acids and organic/inorganic compounds) in human serums, urines and the like.
Many researchers have since then made various efforts to develop novel diagnostic and therapeutic techniques, and the formidable amount of biological information acquired from the completion of global Human Genome Project is now being combined with nanotechnologies. Especially, the carbon nanotubes and semiconductor nanowires are being applied to manufacture a highly sensitive biosensor by using their electric features.
To date, diagnostic sensors using antigen-antibody reaction have been overwhelming in the biosensors market. The antigen-antibody reaction is a highly valuable tool to diagnose diseases with accuracy due to its superior specificity. However, the above method has a disadvantage that antibodies consist of proteins. In detail, certain antibodies are very difficult to produce since they require a very complicated condition of culture and synthesis. Further, the characteristics of antibodies may slightly differ from each another depending upon the batches from which they are prepared and they are also too expensive to be distributed widely for commercial use.
Further, the biosensors using the antigen-antibody reaction are much restricted in terms of their valid length of distribution due to stability problem. The unstable nature of proteins increases the unit production cost and may also generate errors in a diagnostic sensor during operation.
Therefore, there is a need to develop a new diagnostic sensor which has an excellent stability and cost-effectiveness while having an excellent substrate-specificity comparable to or even greater than that of antibodies.